Fluid And Nutrient Delivery System And Associated Methods

ABSTRACT

A system and method for efficiently delivering an aqueous solution to plants includes a microporous hydrophobic tubing coated with a hydrophilic polymer that has a delivery portion positionable adjacent a root system of a plant and a lumen for channeling an aqueous solution from an inlet to the delivery portion. The tubing along the delivery portion has a porosity adapted for permitting a flow of the aqueous solution therethrough when acted upon by a surfactant root exudate generated by the roots due to water stress. A pressure regulating device is upstream of the tubing&#39;s inlet, and a reservoir adapted for holding the aqueous solution therein is situated in fluid communication with an upstream end of the pressure regulating device. Additional tubing can be provided for channeling a nutrient solution to the plant roots.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of patent application Ser. No.11/930,304, filed Oct. 31, 2007, now U.S. Pat. No. 7,748,930, whichitself is a continuation-in-part of patent application Ser. No.11/677,642, filed Feb. 22, 2007, now U.S. Pat. No. 7,712,253, whichitself is a continuation-in-part of patent application Ser. No.11/126,073, filed on May 10, 2005, now U.S. Pat. No. 7,198,431, whichitself claims priority to provisional application Ser. No. 60/569,262,filed on May 10, 2004, the disclosures of all of which are incorporatedby reference hereinto.

FIELD OF INVENTION

The present invention generally relates to systems and methods forwatering and supplying nutrients to plants, and, in particular, to suchsystems and methods for minimizing water use and maximizing potentialcrop density by delivering water and nutrients “on demand.”

BACKGROUND

The need for a self-watering system for plants is well established,since agriculture utilizes approximately 70% of the world's fresh waterresources, and many products have been designed and built to satisfythis need to varying degrees. Some systems supply a small continuousamount of water, often referred to as drip irrigation or trickleirrigation, supplying water to the root zone irrespective of the plants'needs. Other systems rely on the moisture level in the soil to signalthe need for water. Still others use wicks that bring water to the plantas a result of surface tension and the capillary rise effect.

Drip irrigation or trickle irrigation is a well established method ofgrowing crops in arid areas. It is claimed to be 90% efficient in waterusage compared to 75-85% for sprinkler systems. The basic dripirrigation system generally consists of a surface tube from which smalldripper tubes/emitters are fitted to take water from the supply tube tothe roots of the plant on either side of the supply tube. The drippertube/emitter limits the flow of water to the roots drop by drop based onthe viscous resistance to water flow within the emitter/dripper tube.The drip rate is determined by the calculated needs of the specificplants, the soil conditions, anticipated rainfall, andevapotranspiration rate, and can vary from 1 to 4 L/hr per plant.

The need to estimate the water requirements of the crops or the amountof nutrients to be supplied in the water is seldom exact and invariablyleads to wastage of water. It was shown that the roots of plants cancontrol the release of water that is stored behind a thin poroushydrophilic membrane that is believed to become hydrophobic due to theadsorption of organic impurities in the water. The mechanism is notfully understood, though it has been speculated that among the rootexudates is a surfactant that opens the pores of the membrane thatbecame hydrophobic due the adsorbed organic impurities in water. Thehydrophobic membrane inhibits the flow of water to the plants. However,the roots of the plants exude a variety of chemicals that include asurfactant that open the pores of the membrane by making it hydrophilic.Thus water can now flow to the roots and the membrane becomeshydrophobic when the plant has had enough water.

It has also been shown that when two reservoirs (one with water and theother containing nutrient solution) with membranes are presented to aplant, the plant can distinguish between the two sources, taking as muchwater as it needs and as much nutrients as it requires. The ratio ofwater to nutrient can vary from 2-5 to 1 depending on the concentrationof the nutrient solution.

Several sub surface systems have been developed that include tubes thatare porous or are perforated to permit the continuous slow release ofwater. However, these hydrophobic tubes, which require a water pressureof up to two atmospheres, do not automatically stop the delivery ofwater when the plants have had enough or, for example, when it rains.

One possible reason for the absence of a commercial irrigation systemusing the membrane system may be the difficulty of obtaining a membranethat can supply the necessary amount of water for new plants orseedlings as well as a fully grown and mature plant that is sproutingand producing fruit and produce. Another possible reason may be thereliance on constant trace amounts of organic solutes in the water,which become adsorbed on the exit walls of the hydrophilic pore channelsof the membrane, converting the membrane into a hydrophobic system,which then stops or greatly reduces the flow of water through themembrane. Another reason may be the difficulty of obtaining hydrophilictubes of suitable wall thickness and diameter that are sufficientlydurable to make the process economical.

The Russian SVET space plant growth system consists of a box greenhousewith 1000 cm² growing area with room for plants up to 40 cm tall. Theroots were grown on a natural porous zeolite, with highly purified waterkeeping the roots at the required moisture level. Zero-gravity growthchambers used by NASA have included a microporous ceramic or stainlesssteel tube through which water with nutrient is supplied to irrigate thegreenhouse plants. Systems using porous ceramic, stainless, orhydrophobic membranes to deliver water and/or nutrients to plants arebasically a form of drip irrigation where the water/nutrients are alwaysdelivered whether the plants need it or not. As will be apparent to oneof skill in the art, the ceramic or stainless tubes are thicker and theorganic components are adsorbed onto the full length of the channels andcannot be removed by the plant's exudates.

FIG. 7 shows the flow of water and nutrient solution for a single plant.FIG. 7, in particular, is a daily record of water flow (in mL/day)through 12 cm² of microporous Amerace A-10 fitted to the bottom of two285-mL identically sized and shaped reservoirs (No. 1 for water and No.2 for nutrient solution) that were embedded in the potting soil of awell-established Ficus indica (insert), showing the effect on thepattern of water flow when (I) root contact with the membrane wasestablished, and (ii) when the total flow ceased to be greater than therate of water uptake (after day 24). In general, the flow of water isabout three times larger than from nutrient solution. It has been shownthat a change in the concentration of the nutrient alters the ratio offlow from the two reservoirs. In FIG. 7, the exudates from the plant'sroots convert step 3 back to step 1 in FIG. 8. This has been shown in anexperiment by allowing a membrane to close after a specified volume ofwater was passed through an Amerace-10 membrane. The exit side of themembrane was then washed with alcohol and the water flow through themembrane resumed and eventually stopped when all the alcohol was washedaway and the organic impurities were allowed to be adsorbed onto theexit wall of the pores shown in FIG. 8.

Again referring to FIG. 8, in step 1, as water leaves the pore of themembrane, it spreads out onto the membrane's surface, which ishydrophilic. A large drop forms and leaves the surface. As the surfacebecomes coated by the adsorbed hydrophobic impurities in water, thewater leaving the capillary pore of the membrane cannot spread out overthe surface and a smaller drop can be formed (step 2). When furthercoating continues, there is no room for the water to spread out onto thesurface and a greater force is required to push the water through thehydrophobic area shown in step 3. The membrane is converted from thehydrophilic state to a hydrophobic state. It is made hydrophobic by theadsorption of the organic impurities in the water and/or nutrientsolution. This closes the pores and prevents water from leaving themembrane under the prevailing pressure conditions. If the pressure isincreased, it becomes possible for the liquid to flow again because thesurface tension of water no longer can prevent the water from breakingthrough the pores.

SUMMARY OF THE INVENTION

The present invention is directed in one aspect to a system forefficiently delivering an aqueous solution to plants. The systemcomprises hydrophilic means having a distal portion positionableadjacent a root system of a plant. The hydrophilic means have a lumentherethrough for channeling an aqueous solution from an inlet to thedistal portion. The hydrophilic means further have a wall encompassingthe lumen. At least a portion of the wall along the distal portion has aporosity adapted for permitting a flow of the aqueous solutiontherethrough when acted upon by a surfactant root exudate generated bythe plant roots' experiencing water stress.

The system also comprises a reservoir that is adapted for holding theaqueous solution therein. The reservoir is situated in fluidcommunication with the hydrophilic means inlet. Positioned between thereservoir and the hydrophilic means, in one embodiment, is a pressureregulating device for providing at least a minimum pressure value topermit fluid to flow through the hydrophilic means and at most a maximumpressure value above which fluid would flow through the hydrophilicmeans even in the absence of surfactant root exudate.

The present invention is also directed in another aspect to a method forefficiently delivering an aqueous solution to plants. This aspect of themethod comprises the step of positioning a distal portion of hydrophilicmeans adjacent a root system of a plant as described in the systemabove. The aqueous solution is introduced into an inlet of thehydrophilic means, and the aqueous solution is channeled from thehydrophilic means inlet to the distal portion. In a particularembodiment, a pressure of the aqueous solution is regulated upstream ofthe hydrophilic means inlet.

The present invention is further directed in another aspect to a methodfor establishing an efficient system for delivering an aqueous solutionto plants. This aspect of the method comprises the step of positioning adistal portion of hydrophilic means adjacent a root system of a plant,as described above.

The pressure of the aqueous solution is regulated upstream of thehydrophilic means inlet, and a reservoir upstream of the pressureregulation for holding the aqueous solution therein is provided. Achannel is also provided for establishing a flow of the aqueous solutionfrom the reservoir to the hydrophilic means inlet.

The features that characterize the invention, both as to organizationand method of operation, together with further objects and advantagesthereof, will be better understood from the following description usedin conjunction with the accompanying drawing. It is to be expresslyunderstood that the drawing is for the purpose of illustration anddescription and is not intended as a definition of the limits of theinvention. These and other objects attained, and advantages offered, bythe present invention will become more fully apparent as the descriptionthat now follows is read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1A and 1B illustrate a dual irrigation tube for supplying waterand nutrient to plant roots, in top plan view and cross-sectional view,respectively.

FIG. 1C is a cross-sectional view of tubing having a supporting spiralinserted thereinto.

FIG. 2 is a cross-sectional view of a system for irrigating grass.

FIG. 3 illustrates an exemplary system for growing plants that isoperable in a gravity-free environment.

FIG. 4 is a side perspective view of an embodiment of a tube havingholes covered with a hydrophilic membrane.

FIGS. 5A and 5B illustrate a growth system that includes both surfaceand subsurface portions, in top plan view and cross-sectional view,respectively.

FIG. 6 is a chemical diagram of polyhydroxystyrene.

FIG. 7 (prior art) graphs the flow of water and nutrient solution for asingle plant. (•), Water uptake from reservoir No. 1; (V), nutrientuptake from reservoir No. 2. (From L. A. Errede, Ann. Botany 52, 22-29,1983.)

FIGS. 8A-8L (prior art; collectively referred to as FIG. 8) areschematic representations of water flow through a microcapillary pathwayof a microporous membrane as a function of the extent of hydrophilicarea that surrounds the microcapillary outlet, and show how the organicimpurities in water are more likely to stick at the exit end of acapillary. In step 1 (FIGS. 8A-8D) is shown the initial hydrophilicstate of the area that surrounds the microcapillary outlet. D₁ is thediameter of the hydrophilic area, and R₁ is the radius of the dropemerging from the outlet, which is much greater than r, the radius ofthe microcapillary outlet. Step 2 (FIGS. 8E-8H) occurs after someaccumulation of hydrophobic solutes at the outer perimeter of thehydrophilic area that rings the microcapillary outlet. Here D₁>D₂>2r,and R>R₂. Step 3 (FIGS. 8I-8L) is the ultimate end state when thediameter D_(f) of the hydrophilic area that surrounds the outlet shrinksto twice the radius r of the outlet. Water flow at a given outlet stopswhen ΔP=2γ/R_(f) becomes greater than P_(f), the applied pressure, whereγ is the surface tension of the water. (From L. A. Errede, J. ColloidInterface Sci. 100, 414-22, 1984.)

FIG. 9 is a schematic diagram of a system having a pressure regulatingdevice incorporated thereinto.

FIG. 10 is a schematic diagram of an exemplary pressure regulatingdevice for use in the system of FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A description of the preferred embodiments of the present invention willnow be presented with reference to FIGS. 1-10.

As used herein, the words “tubes” or “tubing” refer to supply lines forproviding water and/or nutrients. As will be appreciated by one of skillin the art, such “tubes” or “tubing” do not necessarily need to becylindrical, but may be of any suitable shape, and no limitation isintended by the use of these words.

Described herein are a system and method of supplying water and/ornutrients to the roots of growing plants wherein the water and/ornutrients are released to the plants as needed by the individual plants.Herein the term “plants” should be construed broadly, and can include,for example, grasses. Although not intended as a limitation on theinvention, it is believed that when under water stress, plant roots canemit exudates or surfactants that promote the release of water and/ornutrients stored under the conditions described below. Specifically, theplants are supplied water and/or nutrients from supply lines or feedertubes, at least portions of which are hydrophilic.

In some embodiments, the tubing may include a plurality of holes thatare covered by hydrophilic membranes; in other embodiments, the entiretubing, the below surface portion thereof, or a significant portionthereof is hydrophilic. In yet other embodiments, the system may includea surface tube that is water impermeable or hydrophobic, the tube beingconnected to a plurality of hydrophilic tubes that can be inserted intoa support medium for supplying the roots.

One or more hydrophilic tubes may be inserted into a quantity of supportmedium such that the tubes are at least partially below the surface ofthe support media. The support media may be selected from any suitablemedium or mixture of media suitable for supporting growing plants androots. Examples, which are not intended as limitations, of such supportmedia can include sand, soil, Rockwool, polyurethane foam, Fleximat™,SRI cellulose-based growth media, and the like. Other suitable mediaknown in the art, such as continuous-fiber growth media, may also beused.

In particular embodiments, plants are planted in the support medium andthe respective tubes are connected to reservoirs containing water,nutrients, or a mixture thereof. In some embodiments, two tubes may feeda row of plants: a water tube and a nutrient tube. As discussed above,it has previously been shown that the plants are capable ofdistinguishing between these tubes. Alternatively, nutrient(s) can beadded to a water reservoir for distribution through a unitary tube.

Thin-walled microporous hydrophilic tubes are not known at present to becommercially available for use as irrigation tubing. In a particularembodiment, hydrophilic materials, including Cell Force™ and Flexi SiI™,may be made into hydrophilic tubes. Alternatively, some existinghydrophobic thin-walled tubes can be made hydrophilic by a process thatuses a water-insoluble hydrophilic polymer (e.g., polyhydroxystyrene,U.S. Pat. No. 6,045,869, incorporated herein by reference; structureillustrated in FIG. 6) as a surface coating. Such solutions applied as acoating to and impregnated with microporous hydrophobic plastic tubinghave been shown not to clog the pores and to remain hydrophilic for manyyears. Thus continuous tubes of Tyvek® (a microporous polyethylenematerial made from very fine, high-density polyethylene fibers, DuPont,Richmond, Va.) in a radius of 5-10 mm (Irrigro International IrrigationSystems) have been used after being made hydrophilic and have been shownto act as a membrane that is responsive to the roots of plants in asubsurface irrigation system.

Tyvek® is available in a plurality of styles, each having differentproperties. Although not intended to be limiting, two particular typeshave been found to be most beneficial for use in the present invention:1059B and 1073B.

As discussed above, it has been shown that hydrophilic membranes canbecome hydrophobic over time owing to organic impurities in the wateradsorbed onto the membrane. Because of the variability of the impuritiesin water, we have added organic substances to the water which can beadsorbed onto the exit pore walls, making the membrane hydrophobic, andthereby reducing the flow of water or nutrient solution through themembrane. Examples of suitable organic substances include, but are by nomeans limited to, humic acid, kerosene, turpentine, pinene, paraffin,and hexadecane. In other embodiments, other suitable C8 C16 saturatedhydrocarbons may be used. The amounts added ranged from 10 ppb to 10 ppmto the irrigating medium. As will be appreciated by one of skill in theart, in some embodiments, the addition of the organic substance may notbe essential, depending on the quality of the water.

When growing crops in soil, the addition of nutrient on a continuousbasis is not essential; however, when growing crops in sand, Fleximat™,or Rockwool, a nutrient solution, for example, any suitable nutrientsolution known in the art such as those commonly used in hydroponicsystems, e.g., Hoegland Solution, Peter's Solution, Miracle-Gro®, orother less dyed fertilizer such as Schultz Export may be added to thewater supply or may be fed directly to the plants in a separate tube, asdescribed above, and thus the roots of the plant can be allowed to takeas much water and nutrient as required. However, for growth inartificial media the inclusion of nutrients and micronutrients isimportant.

FIGS. 1A and 1B illustrate a system 10 that uses twin irrigation tubes11,12 for delivering water and nutrient solution to plants 13 growing ina growing medium 14. In this embodiment 10, the tubes 11,12 are runningthrough the root systems 15 of the plants 13. It has been found inexperiments in both sand and potting soil that the higher theconcentration of nutrients used, the smaller the volume of the nutrientsolution that is released to the roots 15, which is illustrative of thewater conservation achieved by the current invention.

It will be understood by one of skill in the art that the tubes 11,12could be provided as a single composite double-lumen tube withoutdeparting from the spirit of the invention. The diameters of the twoportions could be in a proportion commensurate with a plant'srequirements for water versus nutrient, for example, double the size forthe water tube, although this is not intended as a limitation.

In some embodiments, since subsurface thin-walled microporous tubing canbe collapsed if sufficient pressure is applied, a spiral 60 comprising,for example, plastic, can be incorporated into a tubing such as tubing11 or 12 to form a tube 61 that is more resistant to collapsing (FIG.1C).

FIG. 2 illustrates a system 20 for the irrigation of grass 21 where thesubsurface tubes 22 are spaced 1-2 feet apart and are substantiallycontinuously fed with water under low constant pressure, with nutrientsadded to the aqueous solution as desired.

The irrigation systems and methods described herein are believedsuperior to any other watering system currently in use, and further areindependent of atmospheric pressure, making them usable for astrocultureor micro-gravity conditions, as well as others. In one embodiment of theinvention 30 (FIG. 3), for example, a continuous fiber growth medium 31such as Rockwool or the spongy Fleximat (from Grow Tech) can be used tosupport the plants 32 and their roots 33. In this embodiment 30, both ofthe reservoirs 34 comprise a container 35 that has an interior space 36for holding the water and nutrient solution therein. The containers 35are formed similar to a bellows, and are movable between an expandedstate when containing solution and a retracted state when solution hasbeen removed.

The containers 35 also comprise a filling inlet 37 that is in fluidcommunication with the containers' interior space 36 for adding solutionthereto. Distribution tubes 38 are also in fluid communication with thecontainers' interior spaces 36 and with inlets 39 of the hydrophilictubes 40. This arrangement provides solution to the tubings' lumina 40.The distribution tubes 38 also have check valves 41 therein forpreventing backflow of solution from the tubes 40 toward the containers'interior spaces 36.

Support for plants and their roots can be provided for in the presentsystem under zero gravity, for example, with the use of a monolithiccontiguous material such as Rockwool or Fleximat™, a spongy hydrophilicporous material made by Grow-Tech (Lisbon Falls, Me.) or the newlydeveloped artificial sponge such as, for example, AgriLite (SRIEnviro-Grow Systems, Ontario, Canada). By using these materials tosurround twin microporous hydrophilic irrigating tubes, one supplyingwater while the other supplying a nutrient solution, it is possible toachieve complete conservation of water and nutrients supplied to growingplants. Such a system can also be applied to arid or desert environmentswhere water conservation is desirable.

Early laboratory tests showed that using nutrients in water, it waspossible to grow tomatoes in sand with Amerace A10 membranes 42 (50%silica gel in polyethylene) glued over holes 43 in a subsurface PVC tube44 (FIG. 4). The holes 43 in the PVC tube 44 were 12 mm in diameter,spaced 10 cm apart, drilled in 17-mm-ID rigid PVC tubing. The holes 43are believed to have limited the amount of water and nutrient availableto the growing plant, and the system proved to be inadequate when theplants began to bear fruit and needed more membrane area to supply theplants' requirements. Increasing the total surface area of the membraneby drilling and covering more holes improved the system. However, a bestmode of practicing the invention at the present time favors the use of acontinuous tube. Because of the brittle nature of Amerace, membranetubes made of this material tended to crack and leak.

Tyvek® (DuPont) in tube form has been used for irrigation purposes underelevated water pressure for gardens and row crops. However, thehydrophobic nature of the polyethylene material permits it to act as adrip source of water for plants without any control by the exudates ofthe plant roots. The conversion of a hydrophobic surface to hydrophilichas been described (U.S. Pat. No. 6,045,869) and can be used to makeTyvek® tubing hydrophilic and responsive to the water and/or nutrientneeds of the plant. When the tubing has been made hydrophilic by coatingand impregnating it with an alcohol solution of polyhydroxystyrene, thetubing was found to be permeable to water at much lower pressures, andshowed a decrease in water permeability as the organic compounds inwater are adsorbed onto the exit pore walls. This can be considered a“conditioning phase,” during which permeability can be decreased by asmuch as 80% by the addition of hydrocarbons to the tap water.

The present invention is believed to be the first to provide a pluralityof feeding tubes arranged to extend beneath the surface of a supportmedium to feed a plurality of plants or a row of plants. Furthermore, aclear advantage of tubes comprising a hydrophilic material is that agreater area of the support medium is fed water and nutrients comparedto a single horizontal membrane.

The invention will now be described by way of examples; however, theinvention is not intended to be limited by these examples.

Example 1. A 4 ft. length of Tyvek® tubing (#1053D) was made hydrophilicwith an alcoholic solution of polyhydroxystyrene and submerged in a 4.5ft by 13 cm wide by 10 cm deep planter, covered with soil and connectedto a constant supply of nutrient solution at a constant head of 35 cm ofwater. Ten cherry tomato (Lycopersicon sp.) seedlings were planted ateven distances next to the tube where water and nutrients were supplied.Fluorescent lighting was supplied to the plants for 18 hours per day.The average consumption of water was 75±10 mL/hr when the plants were 15cm high and 125±20 mL/hr when the plants were 25 cm high. When rainfallwas simulated by spraying the bed with 100 mL of water, the consumptionof water dropped to zero for 2 hours and slowly over the next 3 hoursreturned to the normal rate. The plants grew to two feet in height, andnumerous tomatoes were harvested.

At the end of the experiment, the system was examined to determine ifthere was any competition between the plants for space on the membrane.An examination of the root system indicated that the roots encircled themembrane only within about 1-2 inches from the plant stem. Thisindicates that it should be possible to increase the density of plantgrowth to an extent that would only be limited by the photochemical fluxavailable and mutual interference.

When a dual-tube system was used to supply both water and nutrientseparately, the ratio of water consumed to nutrient solution consumedwas approximately 2.5 to 1 for 8 cherry tomato plants in sand. Again,little or no fluctuations were observed when the size of the plantsreached a height of 35 cm.

Example 2. A continuous irrigation tube can be unnecessary for plantssuch as grape vines or kiwi vines that are spread apart from each otherby distances as much as 20 to 40 cm. In these situations 50, it is morepractical to use a main flexible surface distributing tube 51 of from20-30 mm ID, out of which are drawn satellite tubes 52 that feed a shortlength of from 10 to 30 cm, depending of the size of the vine, ofthin-walled microporous hydrophilic irrigating tube 53, closed at itsend 54, surrounding the roots 55 of the vine or bush 56, as illustratedin FIGS. 5A and 5B.

Example 3. A tomato plant was planted in potting soil, into which wasalso placed two 20-cm-long microporous hydrophilic tubes of 1 cm radius.The tubes were connected to reservoirs of water and nutrient which werekept full. The soil remained dry while the plant grew to producenumerous tomatoes.

Example 4. Another experiment was conducted with Tyvex® tubing (#1053B),1.25 m long and 1 cm radius. The tubing was sealed at one end that wasmade hydrophilic with a 3% solution of polyhydroxystyrene (Novolac gradefrom TriQuest) in ethanol. The tubing was submerged in a 1.4-m planter,covered with soil, and connected to a supply of nutrient solution at aconstant head of 35 cm of water. Ten cherry tomato (Lycopersicon sp)seedlings were planted at even distanced next to the tube, by whichwater and nutrients were supplied. The plants grew during theconditioning phase while exposed to fluorescence lighting for 16 hr/day.The average consumption of water was 75±10 mL/hr when the plants were 15cm in height and 125±20 mL/hr when the plants were 25 cm in height.

Rainfall was simulated by spraying the bed with 100 mL water, followingwhich the consumption of water dropped to zero for 2 hours and thenslowly, over the next 3 hours, returned to the normal rate.

The plants grew to 60 cm in height, and an abundance of tomatoes washarvested. At the completion of the experiment, the system was examinedto determine if there had been any competition between the plants forspace on the membrane. An examination of the root system indicated thatthe roots encircled the membrane only within about 2.5-5 cm from theplant stem. This finding would seem to indicate that it should bepossible to increase the density of plant growth to a level only limitedby the light flux available and mutual interference.

It has also been shown that different plants requiring different ratesof water and nutrient can grow together with each being satisfiedindividually without monitoring.

Example 5. When a dual membrane system was used to supply both water andnutrient separately, the ratio of water consumed to nutrient solutionconsumed was approximately 2.5 to 1 for 8 cherry tomato plants in sand.Once again, there was little or no fluctuation observed when the size ofthe tomato plants reached a height of 35 cm.

A planter 115 cm long, 13 cm wide, and 10 cm deep, was set up in agreenhouse with dual-feed membrane tubes for water and nutrient throughthe center of a bed comprising 50 cm of Flexmat and 50 cm of rockwoolseparated by 15 cm of polyurethane foam. The seeds or seedlings ofcanola (Brassica sp), beans (Phaseolus sp), corn (Zea Mays sp), andtomatoes (Lycopersicon sp) were planted in each of their respectivemedia and their growth patterns observed. Growth, which was favored inthe Fleximat, proceeded normally, except for the polyurethane foam, witheach crop growing at its own rate under a light flux of 50-60 mW/cm².Root crops such as carrots (Daucus carota var sativa sp), radishes(Raphanus sativus sp), beets (Beta vulgaris sp), and onions (Allium sp)were grown in soil and peat, while potatoes (Solanum tuberosum sp),parsnips (Pastinaca sativa sp), and parsley (Petroselinum sativum vartuberosum sp) were grown successfully in vermiculite. A cellulosematerial (SRI Petrochemical Co.) can also be used as an artificialgrowth medium.

It was determined that grass (Gramineae sp) can be successfullyirrigated for 3 successive years with submerged tubular membranes spaced40-50 cm apart.

Example 6. In another case, two hydroponic planters (30×30×30 cm) werefitted with a membrane tube for a water/nutrient solution approximately7 cm from the bottom. The media comprised a soil-less mixtureapproximately 25-26 cm deep in the planters. This depth allowed the rootcrops to produce straight tap roots, which is of concern to consumerswhen purchasing vegetables. One planter was seeded with parsnips (Daucuscarota var. sativa sp.). The other planter was seeded with parsley(Petroselinum sativum var. tuberosum var. tuberosum sp.), a dual-purposecrop of foliage and root stocks. Plant competition controlled theover-seeding issue with each planter. The plants received only naturalsunlight, reducing the risk of “bolting.” Extreme warm temperatures werea concern for the health of the plants.

The parsnip roots were straight in growth, and produced a total weightof 38.9 g. The texture and flavor were excellent. The parsley producedstraight tap roots, giving a total weight of 38.3 g. The foliageproduced had longer petioles than usually purchased, yet the totalweight was 58.9 g.

It will be appreciated by one of skill in the art that plants withvarying water requirements can be satisfied by the embodiments of thepresent invention, wherein one continuous porous hydrophilic irrigatingtube is used to allow each plant to take its water requirementsindependently of the other plants. Such requirements are often needed ingreenhouses, where many different plants are cultivated under one roof.

It has also been shown that a hydrophilic irrigation tube with twochannels, one for water and the other for nutrients, can fully satisfythe plants' requirements and also increase the density of the plants,limited only by the sunlight available.

It has also been shown that commercially available thin-walledmicroporous hydrophobic tubes can be converted to hydrophilic tubes andthereby become responsive to plants and their roots. Such tubes mayinclude, but are not intended to be limited to, high-pressure irrigationhoses, although their use in the present invention does not require theuse of high pressure.

It has also been shown how a dual-membrane tube can be incorporated intoa container for one or more plants so that the plants can be fed ondemand both water and nutrients from separate reservoirs and therebyrequire no attention or supervision as long as there is water availablein the tube reservoirs. In a particular embodiment, a diametric ratio of3:1 for the water tube over the nutrient tube is optimal, although thisis not intended as a limitation, and obviously is dependent uponnutrient concentration and plant type.

It has additionally been shown that water systems that are free ofcontaminated organic substances and unresponsive in the irrigationsystem can, by the addition of trace amounts of one or more hydrocarbonsto the water supply, become responsive to the irrigation system.

It has also been shown that the irrigation system of the presentinvention can be used to replace the emitter in a drip irrigationsystem, thereby making the release of water and/or nutrient responsiveto the roots. In a particular embodiment, a factor of from 100 to 500has been found for the difference in water volume used between the knowndrip irrigation systems and that of the present invention.

In yet another embodiment 70 (FIG. 9), a pressure regulating device,such as a float flow control valve 71 (FIG. 10), is interposed betweenthe reservoirs 72,73 and the tubing 74,75. In addition, an inline filter76 may be added to filter out particulate matter. In a particularembodiment, the float control 71 is operative to regulate the pressurebetween 1 and 3 psi, although these values are not intended aslimitations. The pressure value is adjustable, for example, by settingthe float flow control valve at a desired level above the tubing 74,75,for example, 28 inches for a particular tubing material and system.

The exemplary float control valve 71 of FIG. 10, a water inlet 77 feedsinto a top end 78 of a chamber 79 and is affixed to a float 80 thatfloats on a maintained water level 81. Water exits via an outlet 82 at abottom 83 of the chamber 79, and an air vent 84 is supplied to maintainatmospheric pressure. The irrigation tube 74,75 is shown positionedbeneath ground level. The height 85 above the tube's level can beadjusted, and the chamber's volume can be selected based upon desiredflow rates through the system 70, for example.

It has been found that the addition of the float flow control valve 71permits minimal operating pressures to be maintained, and that maximumpressures are not exceeded. Whether the tubing 74,75 be uniform ornon-uniform, a minimum pressure is required for liquid to pass through.If too much pressure is applied, the liquid passes through the pores ofthe tubing 74,75 irrespective of the presence or absence of surfactantroot exudate.

This system 70 permits the maintenance of pressures without the use ofother, more expensive, types of pressure regulators, electronic valves,or flow regulators. The system 70 is easily concealed for landscapingapplications, and yet is sufficiently robust for agriculturalapplications.

Sectors of grass are known to be grown substantially in isolation, forexample, on golf courses wherein the greens are formed withinsoil-filled depressions in the ground and continuously or atpredetermined intervals fed with water and nutrients. In such anarrangement, the system of the present invention can ideally providewater and nutrients to the grass roots on an on-demand basis, therebysaving both water and nutrients, and also ensuring optimal sustenance ofthe greens.

The following Tables 1-4 include data on experiments conducted indoors(Table 1) and outdoors (Table 2), and the flow rates for water andnutrient (Table 3) and for watering results in series and for singleplants (Table 4).

TABLE 1 Indoor experimental conditions Plant Growth medium Feed CommentsCherry tomatoes Soil, sand, vermiculite, Tap water; Greenhouse peat,Rockwool, nutrient Fleximat^(d) and water^(a) Radishes, lettuce,Soil^(b) Dual tubes Greenhouse carrots, tomatoes, beets, onions, spinachParsnips, parsley, In separate pots with Nutrient feed Greenhouse inpotatoes vermiculite deep pots Beans^(c), tomatoes, Rockwool andNutrient feed In greenhouse canola FlexiMat ^(a)Two separate feed linesfor water and nutrients. ^(b)Beets did not mature, although the leaveswere abundant. ^(c)Bean roots appear to crawl all over the planter andthroughout the growth media. ^(d)The system was a model for the growthof plants in the International Space Station.

TABLE 2 Outdoor experimental conditions Growth Plant medium FeedComments Zucchini, garlic, melons, Soil Water Garden, good tomatoes,eggplant, corn^(a) results Grass^(b) Soil Water Visible improvementStrawberries Peat and Vertical plant Indoors and FlexiMat nutrientoutdoors ^(a)Corn, melons did not take and grow. ^(b)Spacing ofirrigation tubes of 1. 1.5, and 2 ft (40-50 cm, 10 ft long).

TABLE 3 Test of Rockwool and FlexiMat in series for Astroculture^(a)Flows, Flows, Flow Test No. side A side B Ratio, W/N 1 W 19 N 4.8 4.2 2N 20.5 W 70.3 3.4 3 W 76 N 14 5.4 4 N 25.4 W 75.1 3.0 5 W 63 N 31 2.0 6W 66 N 36 1.8 7 N 27 W 74 2.7 ^(a)Planter with two tubes, one for water(W), the other for nutrient solution (N). The reservoirs wereinterchanged periodically to cancel any membrane effects. Flow rates inmL/hr; experiment time March 18 to July 16.

TABLE 4 Watering results (mL/hr) for various vegetables (carrots, cherrytomatoes, onions, beets, radishes, spinach) in potted planters in twoseries of five (B and C) compared with single irrigated plant (X)^(a)Time interval Test No. (hr) X B C 1 25 5.4 32.4 16.2 2 25 9.7 41.8 41.73 24 9.4 39.4 35.6 4 24 16.9 21.4 31.9 5 26 24.2 23.2 36.3 6 23 8.6 48.941.9 7 23.5 5.7 51.7 38.3 8 3 21 30.0 12.0 9 24 7.5 33.7 18.9 10 22.5 2656 30.4 11 20 12.6 42.3 42.7 ^(a)Experiment time, February 19 to June 6.

Another aspect of the invention is directed to the making of tubing foruse with a “water-on-demand” system. In one method, sheets of alow-porosity substance are coated with the aforementionedpolyhydroxystyrene, and formed into cylinders by, for example, thermal,ultrasonic, or impulse means.

Although not intended as a limitation, a possible explanation of theoperation of the polyhydroxystyrene polymer (FIG. 6) will now bepresented. First, how the polyhdroxystyrene attaches to the membrane:Polyhydroxystyrene has two groups, an hydroxyl (OH), which ishydrophilic and can hydrogen bond with water, and the styrene groups,which include a benzene ring (—C6H4—) attached to an ethylene group(═CH—CH2—), both of which are hydrophobic and can stick to thehydrophobic polyethylene membrane, leaving the hydrophilic (OH) group,which forms a weak hydrogen bond with water.

As discussed above, the polymer can act as a capillary through themembrane. It has been shown that organic impurities in water are 105-106times more likely to stick at the exit end wall of the capillaries,where there is a gas-liquid-solid equilibrium (i.e.,air-water-membrane). The organic impurities are in equilibrium along thewalls of the capillary, where the equilibrium is only between liquid andsolid. Thus the surface of the exit pores become hydrophobic due to theadsorption of the trace organic impurities in water and/or nutrientsolution.

When a plant is in need of water, it emits chemicals called exudatesthat can include a surfactant that removes the adhering organiccompounds at the exit wall and liquid from the irrigation tube now isallowed to flow. This has been shown for two different membranes in theprior art, as discussed above with reference to FIGS. 7-8L.

High-purity water is free of organic impurities. Some domestic watersupplies are often purified to such an extent that very little organicimpurities remain. This would result in pore closure only after a large,and usually unnecessary, volume of water had passed through themembrane. The result would not be suitable because of the time delaybetween the removal of the organics and their deposition onto themembrane and the closure of the pores. On the other hand, too muchorganic content in the water could result in a delay in opening theclosed pores because of the limited amount of surfactant that isreleased by the roots.

It has been found that in general the membrane area needed for a plantis best supplied by a tube of diameter equal to about a 1-cm radius,with a thickness of 0.5 mm maximum and pore sizes of from 0.1 to 5 μm,with a preferred average of 0.4 μm, although this is not intended as alimitation, and other porosity values can be used. This segment of themembrane is to be in contact with the roots of the plant. Short segmentsof membrane tubing can be supplied with water and/or nutrient solutionby smaller diameter tubing, but care must be taken to prevent air locksin the line. Tubing of 1-cm ID would not be considered too large. Sincethe feed lines are exposed to light (sunlight or artificial lighting),it is necessary to use opaque tubing, or the solar active light willresult in algae formation that can eventually block the pores. It isbelieved that the coating of the hydrophobic membrane is primarily toallow the resulting hydrophilic surface to become hydrophobic and toclose the pores. Leaving the inner pore uncoated would restrict the flowof water through the membrane.

In the foregoing description, certain terms have been used for brevity,clarity, and understanding, but no unnecessary limitations are to beimplied therefrom beyond the requirements of the prior art, because suchwords are used for description purposes herein and are intended to bebroadly construed. Moreover, the embodiments of the apparatusillustrated and described herein are by way of example, and the scope ofthe invention is not limited to the exact details of construction.

Having now described the invention, the construction, the operation anduse of preferred embodiments thereof, and the advantageous new anduseful results obtained thereby, the new and useful constructions, andreasonable mechanical equivalents thereof obvious to those skilled inthe art, are set forth in the appended claims.

1. A system for efficiently delivering a solution to a plant comprising:a microporous tubing comprising a hydrophilic polymer, a deliveryportion of the tubing positionable adjacent a root system of a plant,the tubing having a lumen therethrough for channeling a solution from aninlet to the delivery portion, the tubing having a porosity at least atthe delivery portion adapted for permitting a flow of the aqueoussolution therethrough when acted upon by a surfactant root exudate; anda pressure regulating device positionable in fluid communication at anupstream portion with a source of the solution and at a downstreamportion with the tubing inlet, for providing at least a minimum pressurevalue to permit fluid to flow through the tubing and at most a maximumpressure value above which fluid would flow through the tubing even inan absence of surfactant root exudate.
 2. The system recited in claim 1,wherein the pressure regulating device is adapted to provide a pressurevalue in a range of approximately 1 to 3 psi.
 3. The system recited inclaim 1, wherein the pressure regulating device comprises a float flowcontrol valve.
 4. The system recited in claim 1, wherein the pressureregulating device is adjustable for achieving a plurality of operatingpressures.
 5. The system recited in claim 1, wherein the tubingcomprises a hydrophobic tubing, and the hydrophilic polymer comprisespolyhydroxystyrene, with which the hydrophobic tubing is coated andimpregnated.
 6. The system recited in claim 5, wherein the tubingcomprises a first tubing for delivering water, and further comprising asecond microporous tubing comprising with a hydrophilic polymer having adelivery portion positionable adjacent the plant root system, the secondtubing having a lumen therethrough for channeling a nutrient solutionfrom an inlet to the delivery portion, the second tubing further havinga porosity at least at the delivery portion adapted for permitting aflow of the nutrient solution therethrough when acted upon by asurfactant root exudate, the second tubing in fluid communicationadjacent the inlet with the pressure regulating device downstreamportion, wherein the pressure regulating device is positionable in fluidcommunication at the upstream portion with a source of the nutrientsolution.
 7. The system recited in claim 1, further comprising areservoir comprising the fluid source, the reservoir comprising: acontainer having an interior space for holding the aqueous solutiontherein, the container movable between an expanded state when containingsolution and a retracted state when solution has been removed; a fillinginlet in fluid communication with the container interior space foradding solution thereto; and a distribution tube in fluid communicationwith the container interior space and with the tubing inlet, forproviding solution to the tubing lumen via the pressure regulatingdevice, the distribution tube having a check valve therein forpreventing backflow of solution from the tubing lumen toward thecontainer interior space.
 8. A method for efficiently delivering anaqueous solution to a plant comprising: positioning a delivery portionof microporous hydrophobic tubing comprising a hydrophilic polymeradjacent a root system of a plant, the tubing having a wall encompassinga lumen, the tubing further having a porosity at least at the deliveryportion adapted for permitting a flow of an aqueous solutiontherethrough when acted upon by a surfactant root exudate; regulating apressure of the aqueous solution upstream of an inlet of the tubing;introducing the regulated-pressure aqueous solution into the tubinginlet; and channeling the aqueous solution from the tubing inlet to thedelivery portion.
 9. The method recited in claim 8, wherein the polymercomprises polyhydroxystyrene.
 10. The method recited in claim 8, whereinthe pressure regulating step comprises providing a pressure value in arange of approximately 1 to 3 psi.
 11. The method recited in claim 8,wherein the pressure regulating step comprises using a float flowcontrol valve upstream of the tubing inlet.
 12. The method recited inclaim 8, further comprising the step of adjusting a pressure to whichthe aqueous solution is regulated, for achieving a plurality ofoperating pressures.
 13. The method recited in claim 8, wherein thetubing comprises a first tube, and further comprising the steps of:positioning a delivery portion of a second microporous hydrophobic tubecoated with a hydrophilic polymer adjacent the plant root system, thesecond tube having a wall encompassing a lumen, the second tube furtherhaving a porosity at least at the delivery portion adapted forpermitting a flow of a nutrient solution therethrough when acted upon bya surfactant root exudate; introducing the regulated-pressure aqueoussolution into the second tube inlet; and channeling the nutrientsolution from the second tube inlet to the second tube delivery portion.14. A method for establishing a water- and nutrient-delivery system fora plant comprising the steps of: joining lateral ends of a hydrophilicsheet comprising a hydrophilic polymer to form a tube; positioning adelivery portion of the tubing in an artificial plant growth medium;planting a plant in the growth medium, a root system of the plantadjacent the tubing delivery portion; positioning an inlet of the tubingat a proximal end thereof in fluid communication with a source of anaqueous solution; and regulating a pressure of the aqueous solutionupstream of the tubing inlet.
 15. A method for establishing a water- andnutrient-delivery system for a plant comprising: introducing ahydrophilic polymer to a microporous hydrophobic sheet; joining lateralends of the sheet to form a tube; positioning a delivery portion of thetubing in an artificial plant growth medium; planting a plant in thegrowth medium, a root system of the plant adjacent the tubing deliveryportion; positioning an inlet of the tubing in fluid communication witha source of an aqueous solution; and regulating a pressure of theaqueous solution upstream of the tubing inlet.
 16. A method forefficiently delivering an aqueous solution to a plant comprising:positioning a delivery portion of microporous hydrophobic tubingcomprising a hydrophilic polymer adjacent a root system of a plant, thetubing having a wall encompassing a lumen, the tubing further having aporosity at least at the delivery portion adapted for permitting a flowof an aqueous solution therethrough when acted upon by a surfactant rootexudate; regulating a pressure of the aqueous solution upstream of thetubing inlet; introducing the pressure-regulated aqueous solution intoan inlet of the tubing; and channeling the aqueous solution from thetubing inlet to the delivery portion.
 17. The method recited in claim16, wherein the polymer comprises polyhydroxystyrene.
 18. The methodrecited in claim 16, wherein the tubing comprises a first tube, andfurther comprising: positioning a delivery portion of a secondmicroporous hydrophobic tube coated with a hydrophilic polymer adjacentthe plant root system, the second tube having a wall encompassing alumen, the second tube further having a porosity at least at thedelivery portion adapted for permitting a flow of a nutrient solutiontherethrough when acted upon by a surfactant root exudate; regulating apressure of the nutrient solution upstream of an inlet of the secondtube; introducing the pressure-regulated nutrient solution into an inletof the second tube; and channeling the nutrient solution from the secondtube inlet to the second tube delivery portion.
 19. A method forefficiently delivering an aqueous solution to a plant comprising:positioning a delivery portion of microporous hydrophilic tubingcomprising a hydrophilic polymer adjacent a root system of a plant, thetubing having a wall encompassing a lumen, the tubing further having aporosity at least at the delivery portion adapted for permitting a flowof an aqueous solution therethrough when acted upon by a surfactant rootexudate; regulating a pressure of the aqueous solution upstream of aninlet of the tubing; introducing the pressure-regulated aqueous solutioninto the tubing inlet; and channeling the aqueous solution from thetubing inlet to the delivery portion.
 20. The method recited in claim19, wherein the polymer comprises polyhydroxystyrene.
 21. The methodrecited in claim 19, wherein the tubing comprises a first tube, andfurther comprising: positioning a delivery portion of a secondmicroporous hydrophobic tube comprising a hydrophilic polymer adjacentthe plant root system, the second tube having a wall encompassing alumen, the second tube further having a porosity at least at thedelivery portion adapted for permitting a flow of a nutrient solutiontherethrough when acted upon by a surfactant root exudate; regulating apressure of the nutrient solution upstream of the an inlet of the secondtube; introducing the pressure-regulated nutrient solution into thesecond tube inlet; and channeling the nutrient solution from the secondtube inlet to the second tube delivery portion.